FIG. 3 shows a prior art semiconductor analyzer used for energy analysis of radiation (.gamma. rays, X rays, and charged particles). As shown in FIG. 3, the n type semiconductor 11 - metal 13 junction portion or the p type semiconductor 13 - n type semiconductor 11 junction portion has a depletion layer 12. A voltage is applied to the analyzer and almost all of the voltage appears across the depletion layer 12. Furthermore, the thickness of the depletion layer 12 is larger than the range of the incident radiation.
The device is operated as follows.
When incident radiation reaches the depletion layer 12, electron and hole charge carrier pairs are generated, and they are collected at the electrodes by the applied electric field. The energy of charges collected is proportional to the energy E of the incident radiation, and energy analysis of the radiation can be carried out. Herein, the factors limiting the resolution of the energy analysis are as follows.
(a) The statistical error N.sup.1/2 for the number N of generated electron-hole pairs,
(b) Fluctuation of the radiation energy consumed other than in the generation of electron-hole pairs,
(c) Thermal noise and fluctuation inherent in the characteristics of the detection system.
Among the above-described factors that of (a) can be estimated. When a semiconductor detector comprising silicon is used, the energy W required to generate an electron-hole pair is 3.6 eV, and when radiation of E=1 MeV is detected, approximately N=E/W electron-hole pairs are generated. The distribution N is a normal distribution of .sigma.=N.sup.1/2, and the energy resolution .DELTA.E follows when it is represented by a half value width is EQU .DELTA.E =2.36.sigma..multidot.W=2.36(EW).sup.1/2 =4 KeV (1)
Generally, .DELTA.E is about 10 KeV because of the above-described factors (b) and (c). Thus, .DELTA.E / E becomes about 10.sup.-2.
A prior art radiation energy analyzer of such a construction has the following drawbacks.
1. A resolution .DELTA.E/E of only about 10.sup.-2 is obtained because of the above-described factors (a), (b), and (c).
2. The device utilizes a surface barrier and a junction which are likely to deteriorate when the temperature rises. The surface barrier deteriorates above 100.degree. C., and the junction deteriorates at about room temperature. Therefore, it is not possible to bake out gases or to maintain the device at an ordinary temperature. Yet, gas exhaustion is inevitably required when an analyzer is attached to an apparatus of an ultra high vacuum of such as 10.sup.-10 Torr.